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Progettazione impilabile di schede PCB
Blog PCB
Progettazione impilabile di schede PCB

Progettazione impilabile di schede PCB

2022-01-20
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Author:pcb

1. General principles of layer arrangement:
1.1 Ci sono molti fattori che devono essere considerati per determinare la struttura laminata del Scheda PCB multistrato. In terms of wiring, più strati, the better for wiring, ma anche il costo e la difficoltà di fare tavole aumenteranno. For manufacturers, whether the laminate structure is symmetrical or not is the focus that needs to be paid attention to when manufacturing PCB boards, so the selection of the number of layers needs to consider the needs of various aspects to achieve a balance. For experienced designers, after completing the pre-layout of components, si concentreranno sull'analisi dei colli di bottiglia di routing della scheda PCB. Combine other EDA tools to analyze the wiring density of the circuit board; then combine the number and types of signal lines with special wiring requirements such as differential lines, linee di segnale sensibili, etc. determinare il numero di strati dello strato di segnale; poi secondo il tipo di alimentazione, isolation and anti-interference requirements to determine the number of inner electrical layers. In questo modo, the number of layers of the entire circuit board is basically determined.
1.2 The ground plane below the component surface (the second layer) provides the shielding layer of the device and the reference plane for the top wiring; the sensitive signal layer should be adjacent to an internal electrical layer (internal power/ground layer), using the large copper of the internal electrical layer. Pellicola per fornire schermatura per lo strato del segnale. The high-speed signal transmission layer in the circuit should be a signal intermediate layer and sandwiched between two inner electrical layers. In this way, the copper films of the two inner electric layers can provide electromagnetic shielding for high-speed signal transmission, and at the same time, the radiation of the high-speed signal can be effectively limited between the two inner electric layers, so as not to cause external interference.
1.3 All signal layers should be adjacent to the ground plane as much as possible;
1.4 Try to avoid two signal layers directly adjacent to each other; crosstalk is easily introduced between adjacent signal layers, resulting in circuit failure. L'aggiunta di un piano di terra tra i due strati del segnale può efficacemente evitare il crosstalk.
1.5 The main power supply should be adjacent to it as far as possible;
1.6 Take into account the symmetry of the laminated structure.
1.7 For the layer layout of the motherboard, la scheda madre esistente è difficile da controllare cavi paralleli a lunga distanza. For the board-level operating frequency above 50MHZ (the case below 50MHZ can be referred to, and appropriate relaxation), the recommended layout principles:
The component surface and the welding surface are complete ground planes (shielding); there are no adjacent parallel wiring layers; all signal layers are adjacent to the ground plane as much as possible; key signals are adjacent to the ground plane and do not cross the partition area. Note: When setting the layers of a specific PCB board, it is necessary to flexibly grasp the above principles. On the basis of understanding the above principles, secondo le esigenze della scheda singola effettiva, such as: whether a key wiring layer, power supply, and ground plane are required. Aspetta, determine the arrangement of the layers, e non strofinarlo forte, or hold on to it.
1.8 Multiple grounded inner electrical layers can effectively reduce ground impedance. For example, the A signal layer and the B signal layer use separate ground planes, che può efficacemente ridurre l'interferenza di modalità comune.

PCB board

2. Commonly used stacked structures:
2.1 4-layer board
The following is an example of a 4-layer board to illustrate how to optimize the arrangement and combination of various stacked structures.
Per schede comuni a 4 strati, there are several stacking methods (top to bottom).
(1) Siganl_1 (Top), GND (Inner_1), POWER (Inner_2), Siganl_2 (Bottom).
(2) Siganl_1 (Top), POWER (Inner_1), GND (Inner_2), Siganl_2 (Bottom).
(3) POWER (Top), Siganl_1 (Inner_1), GND (Inner_2), Siganl_2 (Bottom). Obviously, l'opzione 3 manca di un accoppiamento efficace tra il piano di potenza e il piano di terra e non deve essere utilizzata. So how should option 1 and option 2 be chosen? In circostanze normali, designers will choose scheme 1 as the structure of the 4-layer board. La ragione della scelta non è che l'opzione 2 non può essere utilizzata, but that ordinary PCB boards only place components on the top layer, quindi è più opportuno utilizzare l'opzione 1. However, quando i componenti devono essere posizionati sia sullo strato superiore che inferiore, and the dielectric thickness between the internal power supply layer and the ground layer is large and the coupling is poor, è necessario considerare quale livello ha meno linee di segnale. For scheme 1, there are fewer signal lines on the bottom layer, and a large-area copper film can be used to couple with the POWER layer; on the contrary, if the components are mainly arranged on the bottom layer, lo schema 2 dovrebbe essere utilizzato per fare la scheda.

2.2 6-layer board
After completing the analysis of the laminated structure of the 4-layer board, the following is an example of the combination method of the 6-layer board to illustrate the arrangement and combination of the 6-layer board laminated structure and the preferred method. (1) Siganl_1 (Top), GND (Inner_1), Siganl_2 (Inner_2), Siganl_3 (Inner_3), POWER (Inner_4), Siganl_4 (Bottom). Lo schema 1 adotta 4 strati di strati di segnale e 2 strati di potenza interna/ground layers, che ha più livelli di segnale, which is conducive to the wiring work between components, ma i difetti di questo sistema sono anche più evidenti, which are manifested in the following two aspects.
"Lo strato di potenza e lo strato di terra sono lontani e non completamente accoppiati.
‘¡ The signal layer Siganl_2 (Inner_2) and Siganl_3 (Inner_3) are directly adjacent, e l'isolamento del segnale non è buono, and crosstalk is prone to occur. (2) Siganl_1 (Top), Siganl_2 (Inner_1), POWER (Inner_2), GND (Inner_3), Siganl_3 (Inner_4), Siganl_4 (Bottom). Scheme 2 Compared with scheme 1, the power supply layer and the ground layer are fully coupled, che presenta alcuni vantaggi rispetto al regime 1, but the Siganl_1 (Top) and Siganl_2 (Inner_1) and Siganl_3 (Inner_4) and Siganl_4 (Bottom) signal layers are directly Adjacent, the signal isolation is not good, e il problema del crosstalk facile non è stato risolto. (3) Siganl_1 (Top), GND (Inner_1), Siganl_2 (Inner_2), POWER (Inner_3), GND (Inner_4), Siganl_3 (Bottom). Compared with Scheme 1 and Scheme 2, Scheme 3 reduces one signal layer and adds an internal electrical layer. Although the layers available for wiring are reduced, this scheme solves the common defects of Scheme 1 and Scheme 2.
‘  The power layer and the ground layer are tightly coupled.
‘¡ Each signal layer is directly adjacent to the internal electrical layer, and is effectively isolated from other signal layers, quindi il crosstalk non è facile da verificarsi.
‘¢ Siganl_2 (Inner_2) is adjacent to the two inner electrical layers GND (Inner_1) and POWER (Inner_3), which can be used to transmit high-speed signals. The two inner electrical layers can effectively shield the outside interference to the Siganl_2 (Inner_2) layer and the Siganl_2 (Inner_2) interference to the outside world. Tenendo conto di tutti gli aspetti, scheme 3 is obviously a kind of chemistry. Allo stesso tempo, scheme 3 is also a commonly used laminated structure for 6-layer boards. Attraverso l'analisi dei due esempi di cui sopra, I believe that readers have a certain understanding of the cascading structure, ma in alcuni casi, a certain scheme cannot meet all the requirements, che richiede la considerazione della priorità dei vari principi di progettazione. Unfortunately, because the layer design of the circuit board is closely related to the characteristics of the actual circuit, the anti-interference performance and design focus of different circuits are different, so in fact, these principles do not have a definite priority for reference. But it is certain that design principle 2 (the internal power supply layer and ground layer should be tightly coupled) needs to be satisfied first in the design, e se è necessario trasmettere segnali ad alta velocità nel circuito, then design principle 3 (the high-speed signal transmission layer in the circuit) should be the signal intermediate layer, and sandwiched between the two inner electrical layers) must be satisfied.

2.3 10-layer board
Typical 10-layer PCB design
The general wiring sequence is TOP--GND---signal layer---power layer---GND---signal layer---power layer---signal layer---GND---BOTTOM. The wiring order itself is not necessarily fixed, ma ci sono alcuni standard e principi che lo costringono: per esempio, the adjacent layers of the top layer and the bottom use GND to ensure the EMC characteristics of the board; for example, each signal layer is preferably used as a reference GND layer Plane; the power supply used by the entire single board is given priority to laying a whole piece of copper; the one that is susceptible to interference, high-speed PCB board, e lo strato interno lungo la transizione è preferito, and so on.